1. Field of the Invention
This invention relates to the field of vehicle hill holder devices, in particular to a hill holder that includes a one-way clutch.
2. Description of the Prior Art
Various types of hill holders have been proposed to prevent a vehicle or any wheeled device from rolling backward down an incline. For example, U.S. Pat. No. 4,867,291 describes use of a hill holder in combination with a manual transmission for a motor vehicle. The hill holder includes a releasable one-way clutch that permits a shaft of the transmission to turn in one direction when the transmission is disposed for operation in forward drive and in an opposite direction when the transmission is set to operate in reverse drive. The actuation system selectively engages and releases the clutch depending on the position of a gearshift lever.
Similarly U.S. Pat. No. 4,650,046 describes a hill holder in combination with a transmission gearbox. The hill holder prevents reverse movement of a motor vehicle through operation of a sprag clutch and a conventional hydraulically actuated disc brake. U.S. Pat. No. 5,474,164 describes a hill-hold mechanism that includes a one-way clutch coupled to a transmission input shaft, a toggle link having a friction pad coupled to the transmission output shaft, and a friction band coupled to the one-way clutch for locking the clutch when the toggle link and friction path react to a change in rotation of the output shaft. The mechanism prevents a vehicle from rolling down an incline, but it permits the vehicle to be driven away in the forward drive direction.
Various one-way clutches have been proposed to produce a one-way drive connection between an outer race and inner race. For example, U.S. Pat. No. 6,138,804 describes a one-way clutch having rollers located in pockets between an outer race and inner race, and coiled compression springs located in each pocket for urging the rollers to a side of the pocket where the outer race and inner race are driveably connected.
U.S. Pat. No. 6,206,164 describes a dual-mode, two-way clutch having V-shaped cam faces formed on an inner race and a circumferentially extending raceway formed in the outer race. Roller elements located between the cam faces and race way drivable connect the inner and outer races when the rollers are held on the cam face. Radial gaps are formed between the rollers and the outer race. The rollers are retained within pockets formed in a retainer, which includes projections that engage within grooves formed on the inner race. When the retainer is urged toward the inter race by the application of an external force, the projections engage the groove to lock the retainer to the inner race. The rollers are located between the cam faces.
The one-way clutch described in U.S. Pat. No. 6,186,298 includes an outer race having a cam surface, an inner race formed with a track surface facing the cam surface, rollers located between the outer race and inner race, springs biasing the rollers in one circumferential direction, a side plate for holding the rollers and the spring at predetermined intervals along the circumferential direction, and a control member acting on the rollers to lock up the one-way clutch in both directions or one only direction by urging the rollers radially against the outer surface of the inner race or the inner surface of the outer race. This frictionally engages the races or releases the rollers from engagement with the races.